The present invention broadly concerns devices for use in spinal implant systems, particularly those using spinal rods contoured for connection at various locations along the length of the spinal column. More specifically, the invention concerns an apparatus for spanning between spinal rods to support vertebral fixation elements of the implant system which provide direct engagement to vertebrae of the spinal column.
Several techniques and systems have been developed for use in correcting and stabilizing spinal curves and facilitating spinal fusion. In one system, a bendable rod is longitudinally disposed adjacent the vertebral column and is fixed to various vertebrae along the length of the column by way of a number of fixation elements. A variety of fixation elements can be provided, such as hooks or bone screws, which are configured to engage specific portions of the vertebra. Typically, two such rod assemblies are used, one on each side of the spinous process or sagittal plane.
An example of one such system is the TSRH.RTM. spinal system of Danek Medical, Inc. In this system, hooks or screws are engaged to the spinal rod by way of eyebolts which are slidably disposed onto the spinal rod and captured within yokes on the fixation elements. A nut is threaded onto a threaded post of the eyebolt to clamp the yoke and rigidly fix the hook or screw element to the spinal fixation rod. Details of the TSRH spinal implant system are disclosed in the "Surgical Technique Manual" provided by Danek Medical, Inc., published in 1990, which disclosure is incorporated herein by reference.
One such construct of the TSRH.RTM. spinal system is shown in FIG. 1. In this construct 10, a pair of bendable spinal rods 11 and 12 extend along the vertebral column of a patient on either side of the sagittal plane or spinous process S. In the illustrated construct, the rods 11 and 12 are adjacent the lumbar vertebrae. These rods are connected to a second pair of rods 13 and 14 which engage the sacrum of the patient. The rods 11 and 13 on the left side of the spinous process S as well as the rods 12 and 14, can be engaged by a plate 15, which can be constructed as the CROSSLINK.RTM. lock plates 804-010 or 804-043 manufactured by Danek Medical, Inc. as part of its TSRH.RTM. system.
A number of vertebral fixation elements are fixed to the spinal rods along the length of the rods. For example, spinal hooks 16 can be disposed at certain positions along the right or left rods. These hooks can be similar to the Danek pedicle hooks 808-004 components of the TSRH.RTM. system. In addition, the vertebral fixation elements can be bone-engaging screws 17, such as the Danek anterior spinal screws sold as product number 808-225.
It has been discovered that in the post-operative period before fusion of the vertebrae occurs, a significant amount of motion can occur between the rods and the vertebral fixation elements, which motion can diminish the corrective effects of the spinal instrumentation 10. Thus, means are provided in the TSRH.RTM. system to laterally connect the rods across the sagittal plane to form a rigid "quadrilateral" construct. This means can include a plate 18, such as the CROSSLINK.RTM. plate produced by Danek Medical. This plate, as is described more fully in the above referenced "Surgical Technique Manual", rigidly interconnects the opposite rods to reduce the loss of correction that occurs over time. The plates 18 and 19 connected at distal locations along the rods are engaged to the rods by way of the same eyebolt assemblies 20 that are used to engage the vertebral fixation elements to the rod.
It is the goal of the surgeon using such spinal implant systems to apply the vertebral fixation elements (hooks and/or screws) to the spine in the appropriate anatomic position, and then to engage each fixation element to the spinal rod. Once the spinal implant system is assembled it is then possible to correct anatomical deformities and stabilize the spine. In the ideal circumstance, the fixation elements are located in a colinear position substantially parallel to the sagittal plane S. However, in many circumstances particular vertebrae may deviate from this colinear position. Under these circumstances, it is often necessary to contour the rod to account for abnormal lateral curvatures of the spine, such as scoliotic curvatures. After the rod has been contoured as dictated by the anatomy, the fixation hooks or bone screws can be engaged directly to the laterally offset vertebrae.
One difficulty with spinal fixation systems of the prior art, and particularly those utilizing spinal rods, is that lateral contouring of the rod in the sagittal plane can often be difficult, particularly since the rod must also be contoured to the normal cervical and lumbar curvatures of the spine. Three dimensional rod contouring is often physically difficult and is sometimes not possible in the space available for a particular patient.
The contouring required to accommodate the abnormal curvatures of the spine being treated often poses problems for engaging the vertebral fixation elements between the rod and the particular vertebra. This problem is particularly difficult with respect to bone screws. It has been found that fixation of the bone screws to the vertebra in a somewhat lateral approach is often preferable since it provides a more secure fixation at the pedicle of the vertebra and minimizes the risk to the spinal cord canal. However, typical spinal rod systems, such as the TSRH.RTM. system illustrated in FIG. 1, do not readily accommodate this partial lateral approach to engaging the bone screw between the vertebra and the spinal rod. Moreover, these systems are not easily adapted to the varying pedicle entry angles afforded at the different vertebral levels. Another drawback of systems such as the system 10 in FIG. 1 is that a number of different components are required to engage the vertebrae and to rigidly interconnect the opposite spiral rods across the sagittal plane.
It would therefore be desirable to have a more streamlined system with a minimum of separately implanted components to not only reduce the amount of time required to implant the system, but to also reduce the irritation to the surrounding soft tissue of the patient.
It is also desirable to have a spinal fixation system that is readily adapted to provide lateral coupling between spinal rods at multiple stages or segments of the spinal column. Such a system should provide this segmental interconnection without interfering with vertebral areas available for bone grafting to achieve permanent fixation or immobilization of damaged vertebrae.
There is currently no system known to the inventor that addresses each of these features in a single apparatus. There is further no known system that adequately provides for mounting a vertebral fixation element, such as a spinal screw, at a number of variable positions relative to the spinal rod, or that permits selective orientation of the fixation element through a number of degrees of freedom. The present invention addresses these needs as well as provides other benefits not previously found in spinal fixation systems of the prior art.